1. Field of the Invention
The present invention relates generally to metal melting furnaces, and specifically to a surge controller for a combustion air blower for supplying combustion air to a vertical shaft furnace for the continuous melting of metal.
2. Description of the Prior Art
In the prior art, there are many types of vertical furnace arrangements that have been used for melting various types of charge materials under a wide variety of different circumstances, such as the typical units disclosed in U.S. Pat. Nos. 2,203,163; 2,815,278; 2,886,304; 3,148,973; 3,199,977; 3,603,571; and, 3,958,919. U.S. Pat. Nos. 3,715,203; 3,788,623; and 3,809,378 generally disclose specific types of furnace arrangements that are particularly useful in melting non-ferrous metals such as copper.
Modern industrial heating processes and especially metal melting furnaces require burners which have a number of characteristics. Burners may be classified into three basic types, depending on the method of mixing the fuel and air.
The simplest arrangement, often called a throat-mix burner, consists of admitting the fuel and air into the combustion chamber through separate ports, usually adjacent to each other, and allowing the two to mix and burn in the furnace. This method of burning produces large, relatively slow-moving flames and has been widely used in firing open hearth steel furnaces.
A second type of mixing is found in the inspirator type of burner wherein the fuel is delivered to the burner under pressure and is discharged from a nozzle or jet in such a way that its momentum is used in mixing the fuel with indrawn air.
The third type of burner involves premixing all or part of the air with the fuel prior to delivery to the burner. With this arrangement the burner itself may be a nozzle designed to deliver the combustible mixture without backfire or flame blowoff. U.S. Pat. No. 4,211,555 discloses such a premixing system.
Within the prior art directed towards burners and their specific structural configurations, many varying types of burners have been designed to operate under a wide variety of particular applications and environments for use in heating a material charge having various individual characteristics. Such burners include those as disclosed in U.S. Pat. Nos. 2,605,180; 3,701,517; 3,852,021; and 4,154,571.
A vertical shaft furnace for the continuous melting of metal is normally fired with a burner of the first or third type above and using a gas fuel, liquid fuel, or a premixed gas or liquid and air fuel. Each type of burner system requires a large amount of combustion air which is usually forced into the system by means of a blower or fan designed to supply a high volume of air at low pressure. See for example, blower 14 or blower 24 of FIG. 1 in the above mentioned U.S. Pat. No. 4,211,555, or the blowers in U.S. Pat. No. 4,301,997, or blower 37 of FIG. 1 of the above mentioned U.S. Pat. No. 3,199,977.
Since melting and processing of metal is not a completely continuous and uniform process due to start-ups, processing interruptions, processing rate adjustments, and shutdown, means for firing a metal melting furnace must have the ability to vary the firing rates. Variations in firing rates cause combustion air demand variations.
Combustion air demand variations are inefficiently compensated for in conventional combustion air blower systems. Typically, the blower is designed to run at maximum capacity with only a slight or no speed regulation possible, resulting in the practice of dumping vast quantities of excess combustion air. Such a conventional system wastes energy, is needlessly noisy because of high velocity air dump, and does not constantly and accurately provide the required consistancy of combustion air pressure.